Thermal displacement correcting apparatus and method for a machine tool

ABSTRACT

A thermal displacement correcting apparatus includes a correction amount estimating device and a parameter automatic selecting device that, in a machine tool having two different sets of specifications that differ due to the presence/absence of a scale and different methods of measuring the lengths of a bed and a table, estimate a thermal displacement correction amount of the machine tool of each set of specifications. The two devices store a collection of parameters for an estimated thermal displacement calculation corresponding to each of the bed, the scale, the table, and a workpiece, as a database, and select the parameters belonging to the set of specifications from the database based on machine information according to each set of specifications, calculate estimated thermal displacements of the bed, the table, and the workpiece, or also the scale, according to the selected parameters, and combine the estimated thermal displacements.

BACKGROUND OF THE INVENTION

This application claims the benefit of Japanese Patent ApplicationNumber 2010-292026 filed on Dec. 28, 2010, the entirety of which isincorporated by reference.

1. Field of The Invention

The present invention relates to a thermal displacement correctingapparatus and a thermal displacement correcting method for a machinetool such as a NC lathe and a machining center.

2. Description of Related Art

The transfer of heat generated at power portions and slide portions andthe like and a change in environment temperature cause thermaldeformation in a machine tool. Because this thermal deformation affectsthe machining accuracy, an apparatus has been proposed that estimatesthe amount of thermal deformation from the machine body temperature andmakes corrections when machining (for example, the apparatus describedin Japanese Patent Application Publication No. JP-A-2006-281335). Thisthermal displacement correcting apparatus estimates and corrects thermaldisplacement between a workpiece and a blade edge using parameters suchas position information, linear coefficient of expansion, andtemperature and the like of a scale, a table, and the workpiece.

When this kind of thermal displacement correcting apparatus is appliedto machines of the same model but with different specifications, theparameters must be prepared for each, which is tedious. That is, evenwith machines of the same model, if the machine specifications aredifferent regarding the presence/absence or mounting position of ascale, or the way in which a table is mounted, the position informationand linear coefficient of expansion and the like of the scale and tablemust be set for each set of specifications and stored in the thermaldisplacement correcting apparatus as a individual parameter files. Asthe number of sets of specifications increases, it becomes more tediousto set the parameters and operate the various parameter files, and therisk of a malfunction from an incorrectly set parameter increases, suchthat productivity and manageability of the thermal displacementcorrecting apparatus become poor.

SUMMARY OF THE INVENTION

Therefore, it is an object of the invention according to first to fourthaspects to provide a thermal displacement correcting apparatus or methodfor a machine tool, that enables setting and operating to be performedaccurately and easily, even if there are a large number of sets ofspecifications.

In order to achieve this object, a first aspect of the invention relatesto a thermal displacement correcting apparatus for a machine tool thathas sets of specifications that differ from one another due to at leastsome estimated elements being different, that includes a correctionamount estimating portion that calculates a thermal displacementcorrection amount of the machine tool of at least one of the sets ofspecifications. The correction amount estimating portion stores acollection of parameters for an estimated thermal displacementcalculation corresponding to each of all of the estimated elements as aparameter group, and is able to read machine information according tothe at least one of the sets of specifications, and selects theparameters corresponding to the estimated elements belonging to the atleast one of the sets of specifications from the parameter group basedon the machine information, calculates an estimated thermal displacementof each estimated element according to the selected parameters, andcalculates the thermal displacement correction amount of the machinetool of the at least one of the sets of specifications by combining theestimated thermal displacements.

In order to achieve this object, a second aspect of the inventionrelates to a thermal displacement correcting apparatus for a machinetool that has sets of specifications that differ from one another due toat least some estimated elements being different, that includes acorrection amount estimating portion that calculates a thermaldisplacement correction amount of the machine tool of at least one ofthe sets of specifications; and temperature sensors that measure atemperature of the estimated elements. The correction amount estimatingportion stores a collection of types of the temperature sensorscorresponding to each of all of the estimated elements as a temperaturesensor selection database, is able to read machine information accordingto the at least one of the sets of specifications, selects the type ofthe temperature sensors corresponding to the estimated elementsbelonging to the at least one of the sets of specifications from thetemperature sensor selection database based on the machine information,calculates an estimated thermal displacement of each of the estimatedelements based on the temperatures of the estimated elements ascertainedby the temperature sensors of the selected type, and calculates athermal displacement correction amount of the machine tool of the atleast one of the sets of specifications by combining the estimatedthermal displacements.

In order to achieve this object, a third aspect of the invention relatesto a method for, in a machine tool that has sets of specifications thatdiffer from one another due to at least some estimated elements beingdifferent, calculating a thermal displacement correction amount of themachine tool of at least one of the sets of specifications, thatincludes storing a collection of parameters for an estimated thermaldisplacement calculation corresponding to each of all of the estimatedelements as a parameter group; reading machine information according tothe at least one of the sets of specifications, and selecting theparameters corresponding to the estimated elements belonging to the atleast one of the sets of specifications from the parameter group basedon the machine information; and calculating an estimated thermaldisplacement of each estimated element according to the selectedparameters, and calculating the thermal displacement correction amountof the machine tool of the at least one of the sets of specifications bycombining the estimated thermal displacements.

In order to achieve this object, a fourth aspect of the inventionrelates to a method for, in a machine tool that has sets ofspecifications that differ from one another due to at least someestimated elements being different, calculating a thermal displacementcorrection amount of the machine tool of at least one of the sets ofspecifications, that includes storing a collection of types oftemperature sensors that measure a temperature of the estimated elementsand that correspond to each of all of the estimated elements as atemperature sensor selection database; reading machine informationaccording to the at least one of the sets of specifications andselecting the type of temperature sensors corresponding to the estimatedelements belonging to the at least one of the sets of specificationsfrom the temperature sensor selection database based on the machineinformation; and calculating an estimated thermal displacement of eachof the estimated elements based on the temperatures of the estimatedelements ascertained by the temperature sensors of the selected type,and calculating a thermal displacement correction amount of the machinetool of the at least one of the sets of specifications by combining theestimated thermal displacements.

According to the present invention, temperature sensors and parameterscorresponding to estimated elements relating to the set ofspecifications of a machine tool for which a correction is to be made,are selected from a database based on machine information. As a result,even if there are a plurality of sets of specifications, it issufficient to simply prepare a common database, so productivity (ease offormulation) and manageability of the thermal displacement correctingapparatus and method become extremely good.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a machine toot and thermal displacement correctingapparatus according to a first example embodiment of the presentinvention.

FIG. 2A is a partial view of FIG. 1, and FIG. 2B is a view of a machinetool with different specifications.

FIG. 3 is a view of a parameter group (parameter database and parameterfile).

FIG. 4 is a flowchart illustrating operation of the machine tool andthermal displacement correcting apparatus shown in FIG. 2.

FIG. 5 is a view of a machine tool and thermal displacement correctingapparatus according to a second example embodiment of the presentinvention.

FIG. 6 is a view of a machine tool and thermal displacement correctingapparatus that are the same models as the machine tool and thermaldisplacement correcting apparatus in FIG. 5 but with differentspecifications.

FIG. 7 is a view showing a frame format of a temperature sensorselection database of the machine tool and thermal displacementcorrecting apparatus in FIGS. 5 and 6.

FIG. 8 is a flowchart illustrating operation of the machine tool andthermal displacement correcting apparatus in FIGS. 5 and 6.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, example embodiments of the present invention will bedescribed with reference to the drawings as appropriate. It should benoted that the example embodiments are not limited to the examples givenbelow.

[First example embodiment]

FIG. 1 is a side view of a machine tool (a portal machining center) towhich a thermal displacement correcting apparatus according to a firstexample embodiment of the present invention has been applied. A bed 1 isarranged along an X-axis (i.e., an axis in the left-right direction inFIG. 1; the right is positive). A table 5 on which a workpiece 6 is ableto be mounted is supported so as to be able to move in the direction ofthe X-axis on the bed 1 via a nut 4.

A column 7 stands on both side surfaces of the bed 1, and a cross rail(not shown) is fixed between the columns 7. A saddle 8 is supported soas to be able to move in the direction of a Y-axis (i.e., an axis in thedirection perpendicular to the surface of the paper in FIG. 1; the nearside is positive) on the cross rail. Furthermore, a main spindle 9 issupported, so as to be able to move in the direction of a Z-axis (i.e.,an axis in the vertical direction of FIG. 1; up is positive), on thesaddle 8, and a tool 10 for machining the workpiece 6 is rotatably fixedto a tip end of this main spindle 9.

FIGS. 2A and 2B are views of portal machining centers of the same modelbut with different specifications. The portal machining center in FIG.2A is the same as the portal machining center shown in FIG. 1. Withthese portal machining centers, the structure related to detecting amovement amount of the table 5 in the direction of the X-axis isdifferent.

According to the specifications in FIG. 2A (referred to as“specifications set A”), the table 5 moves by a ball screw (not shown)combined with the nut 4. The ball screw is rotatably fixed to the bed 1side, and the nut 4 is fixed to the table 5. According to thesespecifications, there is a scale 2 and a slider 3 that form a positiondetector. The scale 2 is fixed to the bed 1, and the slider 3 is fixedto the table 5. A position X of the table 5 is determined by theposition detector by, for example, the slider 3 reading positioninformation indicated by the scale 2 and outputting the positioninformation to an NC device that will be described later.

Meanwhile, according to the specifications in FIG. 2B (referred to as“specifications set B”), the table 5 moves by a ball screw (not shown)combined with the nut 4. The ball screw is rotatably fixed to the bed 1side, and the nut 4 is fixed to the table 5. The position X of the table5 is determined by rotation control (a rotational position detector) ofthe ball screw by, for example, converting a rotational position (numberof rotations), that is detected by the rotational position detector (notshown) arranged on an end portion of the ball screw, to a X position, inthe NC device 15 that will be described later.

As shown in FIG. 1, in specifications set A, temperature sensors 11A to11D that detect the temperature of the bed 1, the scale 2, the table 5,and the workpiece 6 are provided. In addition, a temperature measuringdevice 12 that ascertains the temperatures by receiving signalsindicative of the detected temperatures from the temperature sensors 11Ato 11D, a correction amount estimating device 13 that receivesinformation from the temperature measuring device 12 and a parameterautomatic selecting device 14 and calculates a correction amount relatedto thermal displacement, and the NC device 15 that numerically controlsthe table 5, the saddle 8, and the main spindle 9 and the like areprovided. The parameter automatic selecting device 14 reads machineinformation of the NC device 15 via communication, and automaticallyselects estimated calculation parameters of thermal displacement basedon the read machine information. The correction amount estimating device13 and the parameter automatic selecting device 14 form the thermaldisplacement correcting apparatus according to the present invention,but a combination of these and the temperature sensors 11A to 11D andthe temperature measuring device 12 may also be regarded as the thermaldisplacement correcting apparatus. Also, the correction amountestimating device 13 and the parameter automatic selecting device 14form a correction amount estimating portion according to the presentinvention.

In specifications set B as well, the thermal displacement correctingapparatus is configured just as in specifications set A, but no scale 2is provided, so the temperature sensor 11B related to the scale 2 is notprovided, which differs from specifications set A.

Here, the estimated elements of the machine tool of each set ofspecifications will be described in more detail. With specifications setA, the bed 1, the scale 2, the table 5, and the workpiece 6 can be givenas estimated elements related to the thermal displacement estimation. anthe other hand, with specifications set B, the bed 1, the table 5, andthe workpiece 6 can be given as estimated elements related to thethermal displacement estimation. An estimated element means a mechanicalstructural element that is considered when a thermal displacement of themachine tool is estimated. Further, in specifications sets A and B,regarding the thermal displacement correction, the estimated elementsdiffer in terms of the presence and absence of the scale 2, while theremaining estimated elements are at least the same, but the content ofthe length parameters of the estimated elements differ. That is, inspecifications set A, the positions of the scale 2 and the slider 3 arepart of the length parameter, but in specifications set B, the positionof the nut 4 is part of the length parameter.

FIG. 3 is a view (table) showing a frame format of a database as aparameter group for selecting an estimated calculation parameter storedin the correction amount estimating device 13. This database is commonamong machines of the same model, and is stored in both specificationsset A and specifications set B. Here, δ_(i) represents the thermaldeformation of each estimated element i (the bed 1 if i is A, 1, or bed;the scale 2 if i is B, 2, or scale; the table 5 if i is C, 3, or table;and the workpiece 6 if i is D, 4, or workpiece), α_(i) represents alinear coefficient of expansion of the estimated element i, T_(i)represents a detected temperature of the estimated element i, and L_(i)represents a length of the estimated element i. Also, X represents theposition of a blade edge of the tool 10 on the X-axis, Xa represents theposition of the scale 2 on the X-axis, Xb represents the position of theslider 3 on the X-axis, Xw represents the position of the workpiece 6 onthe X-axis, and Xe represents the position of the nut 4 on the X-axis(see FIG. 2).

This kind of machine tool and thermal displacement correcting apparatusaccording to the first example embodiment mainly operate, estimate thethermal displacement, and execute a thermal displacement correctingmethod as illustrated in FIG. 4.

That is, first, in specifications set A, the temperature measuringdevice 12 receives signals from the temperature sensors 11A to 11Drelated to the estimated elements i, and estimates the temperatures ofthe estimated elements i (step S1).

Next, the parameter automatic selecting device 14 reads the machineinformation from the NC device 15 (step S2). The machine informationhere is identification information indicative of specifications set A,and the parameter automatic selecting device 14 selects the thermaldisplacement parameters related to specifications set A, referencing thedatabase in FIG. 3, based on this machine information (step S3). Morespecifically, the parameter automatic selecting device 14 selects α_(A)to α_(D), T_(A) to T_(D), (Xa−X), (Xb−Xa), (Xw−Xb), and (X−Xw) as thethermal displacement parameters, referencing the columns ofspecifications set A.

Continuing on, the correction amount estimating device 13 receives thethermal displacement parameters selected in step S3, and performs anestimate calculation of the thermal displacement using these thermaldisplacement parameters (step S4). The estimated thermal displacementδ_(i) of each estimated element i is expressed by [Expression 1] below.δ_(i)=α_(i) ·T _(i) ·L _(i)  [Expression 1]Therefore, the relative estimated thermal displacement Δ between theworkpiece 6 and the blade edge of the tool 10 is expressed by[Expression 2] below. Here, n is the number of estimated elements (thataffects the estimated thermal displacement Δ).

$\begin{matrix}{\Delta = {{\int_{1}^{n}\delta_{1}} = {\int_{1}^{n}{\alpha_{1} \cdot T_{1} \cdot L_{1}}}}} & \left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Also, from the thermal displacement parameters selected in step S3, itis evident that the estimated thermal displacement Δ is the sum of A1 (δbed), B1 (δ scale), C1 (δ table), and D1 (δ workpiece) in FIG. 2A. A1 toD1 are as shown in [Expression 3] below, so the estimated thermaldisplacement Δ is as shown in [Expression 4] below.δ bed=α_(A) ·T _(A)·(X _(a) −X)δ scale=α_(B) ·T _(B)·(X _(b) −X _(a))δ table=α_(C) ·T _(C)·(X _(w) −X _(b))δ Work=α_(D) ·T _(D)·(X−X _(w)) −piece  [Expression 3]Δ=α_(A) ·T _(A)·(X _(a) −X)−α_(B) ·T _(B)·(X _(b) −X _(a))−α_(C) ·T_(C)·(X _(w) −X _(b))−α_(D) ·T _(D)·(X−X _(w))  [Expression 4]

When the estimated thermal displacement Δ is calculated in this way, thecorrection amount estimating device 13 outputs the estimated thermaldisplacement Δ to the NC device 15, and the NC device 15 performs movingcontrol taking the received estimated thermal displacement Δ intoaccount (step S5). Also, if the correction is continued, the processreturns to step S1 and the operation continues. If the correction is notcontinued, the process ends (step S6).

On the other hand, with specifications set B, the other steps describedbelow operate the same as with specifications set A. That is, when themachine information of specifications set B is read in step S2, thethermal displacement parameters related to specifications set B areselected in step S3 (step S3). More specifically, α_(A), α_(C), α_(D),T_(A), T_(C), T_(D), (Xe−X), (Xw−Xe), and (X−Xw) are selected as thethermal displacement parameters, referencing the columns ofspecifications set B. “0” means that there are no parameters.

Then, the estimated thermal displacement Δ is identified as the sum ofA2 (δ bed), C2 (δ table), and D2 (δ workpiece) in FIG. 2B. A2, C2, andD2 are as shown in [Expression 5] below, and the estimated thermaldisplacement Δ is as shown in [Expression 6] below.δ bed=α_(A) ·T _(A)·(X _(e) −X)δ table=α_(C) ·T _(C)·(X _(w) −X _(e))δ Work=α_(D) ·T _(D)·(X−X _(w)) −piece  [Expression 5]Δ=α_(A) ·T _(A)·(X _(e) −X)−α_(C) ·T _(C)·(X _(w) −X _(e))−α_(D) ·T_(D)·(X−X _(w))  [Expression 6]

The thermal displacement correcting apparatus according to the firstexample embodiment described above includes the correction amountestimating device 13 and parameter automatic selecting device 14 that,in a machine tool that has two different sets of specifications thatdiffer due to the presence/absence of the scale 2 and different methodsof measuring the lengths of the bed 1 and the table 5, estimate thethermal displacement correction amount of the machine tool of each setof specifications. The correction amount estimating device 13 and theparameter automatic selecting device 14 store a collection of parametersfor the estimated thermal displacement calculation corresponding to eachof the bed 1, the scale 2, the table 5, and the workpiece 6, as adatabase. In addition, the correction amount estimating device 13 andparameter automatic selecting device 14 are able to read the machineinformation according to each set of specifications, select theparameters (those relating to the bed 1, the scale 2, the table 5, andthe workpiece 6 if specifications set A, with the length measured basedon the scale 2 and the slider 3; and those relating to the bed 1, thetable 5, and the workpiece 6 if specifications set B, with the lengthmeasured based on the nut 4) corresponding to the bed 1, the scale 2,the table 5, and the workpiece 6 belonging to the set of specificationsfrom the database based on the machine information, calculates theestimated thermal displacements of the bed 1, the table 5, and theworkpiece 6 or also the scale 2 according to the selected parameters,and calculates the thermal displacement correction amount of the machinetool of each set of specifications by combining the estimated thermaldisplacements.

Accordingly, one type of the parameter database and the thermaldisplacement correcting apparatus may be prepared for each machine toolof the same model, regardless of the specifications. It is no longernecessary to prepare a parameter database and change the parametersettings for each set of specifications, nor is it necessary to operatenumerous types of parameter databases and cross-check with thespecifications in the parameter databases, so the risk of a malfunctionoccurring due to a discrepancy in the parameters and specifications canbe reduced. As a result, productivity and manageability of the thermaldisplacement correcting apparatus related to a machine tool having aplurality of sets of specifications become extremely good.

Also, the thermal displacement correcting method according to the firstexample embodiment is a method for; in a machine tool that has twodifferent sets of specifications that differ due to the presence/absenceof the scale 2 and different methods of measuring the lengths of the bed1 and the table 5, estimating the thermal displacement correction amountof the machine tool of each set of specifications, that includes a stepin which the correction amount estimating device 13 and the parameterautomatic selecting device 14 store a collection of parameters for theestimated thermal displacement calculation corresponding to each of thebed 1, the scale 2, the table 5, and the workpiece 6, as a database inadvance, a step in which the correction amount estimating device 13 andthe parameter automatic selecting device 14 read the machine informationaccording to each set of specifications, select the parameters (thoserelating to the bed 1, the scale 2, the table 5, and the workpiece 6 ifspecifications set A, with the length measured based on the scale 2 andthe slider 3; and those relating to the bed 1, the table 5, and theworkpiece 6 if specifications set B, with the length measured based onthe nut 4) corresponding to the bed 1, the scale 2, the table 5, and theworkpiece 6 belonging to the set of specifications from the databasebased on the machine information, and a step in which the correctionamount estimating device 13 and the parameter automatic selecting device14 calculate the estimated thermal displacements of the bed 1, the table5, and the workpiece 6 or also the scale 2 according to the selectedparameters, and calculate the thermal displacement correction amount ofthe machine tool of each set of specifications by combining theestimated thermal displacements.

Accordingly, it is sufficient to prepare only one type for a parametergroup regardless of the specifications. It is no longer necessary toprepare a parameter database and change the parameter settings for eachset of specifications, nor is it necessary to operate numerous types ofparameter databases and cross-check with the specifications in theparameter databases, so the risk of a malfunction occurring due to adiscrepancy in the parameters and specifications can be reduced. As aresult, ease of formulation and manageability of the thermaldisplacement correcting method related to the machine tool having aplurality of sets of specifications becomes extremely good.

[Second example embodiment]

FIG. 5 is a side view of a machine tool (standard specifications) towhich a thermal displacement correcting apparatus according to a secondexample embodiment of the present invention has been applied. Aheadstock 103 is arranged on a bed 102 on a leg 101. The headstock 103rotatably supports a main spindle 104 that has a chuck (not shown) thatholds a workpiece. Also, a saddle 105 is arranged so as to be able tomove in the axial direction of the main spindle 104 (i.e., in thedirection perpendicular to the surface of the paper on which FIG. 5 isdrawn) on the bed 102, a tool rest 106 is supported so as to be able tomove in the radial direction of the main spindle on the saddle 105, anda turret 108 that holds a tool 107 is provided on the tool rest 106.

Further, temperature sensors ch1 to ch4 are arranged on the bed 102, theheadstock 103, the saddle 105, and the tool rest 106, respectively. Atemperature measuring device 109 that converts analog signals outputfrom these temperature sensors into digital signals and quantifies them,a displacement type calculating device 110 as a correction amountestimating portion that calculates a relational expression of thethermal displacement from the quantified temperature measurement values,a correcting device 111 that obtains a correction amount using thatrelational expression, and a NC device 112 that controls the saddle 105and the tool rest 106 based on the correction amount, are provided.Machine information indicative of the specifications of the machine toolfor which the displacement type calculating device 110 is installed isstored in the displacement type calculating device 110.

FIG. 6 is a view of a machine tool that is the same model as the machinetool and in FIG. 5 but with different specifications in that it also hasa lower tool rest 114 and the like as an estimated element (aconstituent element). That is, this machine tool is the same as themachine tool in FIG. 5, except that a lower saddle 113 is also providedon the bed 102, a lower tool rest 114 is supported so as to be able tomove in the radial direction of the main spindle 104 on the lower saddle113, and a lower turret 116 that holds a lower tool 115 is provided onthe lower tool rest 114. Also, temperature sensors ch5 and ch6 arearranged on the lower saddle 113 and the lower tool rest 114.

FIG. 7 is a table showing a database for a temperature sensor selection(a temperature sensor selection database and temperature sensorselection file). The database is stored in the displacement typecalculating device 110. In this database, information indicating whethera sensor is used with both sets of specifications (“0” in this case),whether a sensor is used only with the set of specifications having thelower tool rest 114 and the like in FIG. 6 (“1” in this case), orwhether a sensor is not used with either of the sets of specifications(“2” in this case), is linked to each temperature sensor ch1 to ch6.

This kind of machine tool and thermal displacement correcting apparatusaccording to the second example embodiment mainly operate, estimate thethermal displacement, and execute a thermal displacement correctingmethod as illustrated in FIG. 8.

In other words, with the standard specifications, the machineinformation corresponding to the standard specifications is read, andthe specifications are understood to be standard specifications (stepS101). Based on this, the temperature sensors ch1 to ch4 given a valueof “0” in the temperature sensor selection database are selected, andthe setting is switched to activate the temperature sensors ch1 to ch4(and deactivate the other temperature sensors ch5 and ch6) (step S102).Then, the temperatures of the structures (in this case, the bed 102, theheadstock 103, the saddle 105, and the tool rest 106) are measured bythe active temperature sensors ch1 to ch4 (step S103), a displacementamount (estimated thermal displacement) is calculated from the measuredtemperatures just as in the first example embodiment (step S104), acorrection amount is calculated (step S105), and a correction iscontinued as appropriate (step S106).

On the other hand, with the different specifications, the machineinformation corresponding to different specifications is read, and it isunderstood that the specifications are different specifications (stepS101). Based on this, the temperature sensors ch1 to ch6 given a valuesof “0” and “1” in the temperature sensor selection database areselected, and the setting is switched to activate the temperaturesensors ch1 to ch6 (step S102). Then, the temperatures of the structures(i.e., the estimated elements, in this case, the bed 102, the headstock103, the saddle 105, the tool rest 106, the lower saddle 113, and thelower tool rest 114) are measured by the active temperature sensors ch1to ch6 (step S103), a displacement amount and a correction amount arecalculated just as with the standard specifications (steps S104 and105), and a correction is continued as appropriate (step S106).

The thermal displacement correcting apparatus according to the secondexample embodiment described above includes i) the displacement typecalculating device 110 that, in a machine tool that has different setsof specifications (i.e., standard specifications and differentspecifications) that differ from one another due to the presence/absenceof the lower saddle 113 and the lower tool rest 114, calculates thethermal displacement correction amount of the machine tool of at leastone of the sets of specifications, and ii) the temperature sensors ch1to ch6 that measure the temperatures of the bed 102, the headstock 103,the saddle 105, the tool rest 106, the lower saddle 113, and the lowertool rest 114. The displacement type calculating device 110 stores acollection of types of the temperature sensors ch1 to ch6 correspondingto all of the bed 102, the headstock 103, the saddle 105, the tool rest106, the lower saddle 113, and the lower tool rest 114, respectively, asa temperature sensor selection database. In addition, the displacementtype calculating device 110 is able to read the machine informationaccording to the set of specifications, selects the types of temperaturesensors ch1 to ch6 (temperature sensors ch1 to ch4 if the standardspecifications, and temperature sensors ch1 to ch6 if the differentspecifications) corresponding to the bed 102, the headstock 103, thesaddle 105, and the tool rest 106 belonging to the set of specificationsfrom the temperature sensor selection database based on the machineinformation. The displacement type calculating device 110 calculates theestimated thermal displacements of the bed 102, the headstock 103, thesaddle 105, and the tool rest 106 (or also the lower saddle 113 and thelower tool rest 114), based on the temperatures of the bed 102, theheadstock 103, the saddle 105, and the tool rest 106 (or also the lowersaddle 113 and the lower tool rest 114) ascertained by the temperaturesensors ch1 to ch4 (or the temperature sensors ch1 to ch6) of theselected types, and calculates the thermal displacement correctionamount of the machine tool of the set of specifications by combining theestimated thermal displacements.

Accordingly, with the thermal displacement correcting apparatusaccording to the second example embodiment, even if the arrangement ofthe temperature sensors is different for each set of specifications, thecommon temperature sensor selection database enables the temperaturesensors used in the set of specifications for which a correction is tobe made to be appropriately selected, so it is no longer necessary tochange the setting related to the temperature sensors for each set ofspecifications. As a result, it is not necessary to spend time with thiskind of setting, so productivity and manageability become extremelygood.

The thermal displacement correcting method according to the secondexample embodiment is a method for, in a machine tool that has differentsets of specifications (i.e., standard specifications and differentspecifications) that differ from one another due to the presence/absenceof the lower saddle 113 and the lower tool rest 114, calculating thethermal displacement correction amount of the machine tool of at leastone of the sets of specifications, that includes a step in which thedisplacement type calculating device 110 stores a collection of types ofthe temperature sensors ch1 to ch6 corresponding to all of the bed 102,the headstock 103, the saddle 105, the tool rest 106, the lower saddle113, and the lower tool rest 114, respectively, as a temperature sensorselection database, a step in which the displacement type calculatingdevice 110 reads the machine information according to the set ofspecifications, and selects the types of temperature sensors ch1 to ch6(temperature sensors ch1 to ch4 if the standard specifications, andtemperature sensors ch1 to ch6 if the different specifications)corresponding to the bed 102, the headstock 103, the saddle 105, and thetool rest 106 (or also the lower saddle 113 and the lower tool rest 114)belonging to the set of specifications from the temperature sensorselection database based on the machine information, and a step in whichthe displacement type calculating device 110 calculates the estimatedthermal displacements of the bed 102, the headstock 103, the saddle 105,and the tool rest 106 (or also the lower saddle 113 and the lower toolrest 114), based on the temperatures of the bed 102, the headstock 103,the saddle 105, and the tool rest 106 (or also the lower saddle 113 andthe lower tool rest 114) ascertained by the temperature sensors ch1 toch4 (or the temperature sensors ch1 to ch6) of the selected types, andcalculates the thermal displacement correction amount of the machinetool of the set of specifications by combining the estimated thermaldisplacements.

Accordingly, with the thermal displacement correcting method accordingto the second example embodiment, even if the arrangement of thetemperature sensors is different for each set of specifications, thecommon temperature sensor selection database enables the temperaturesensors used in the set of specifications for which a correction is tobe made to be appropriately selected, so it is no longer necessary tochange the setting related to the temperature sensors for each set ofspecifications. As a result, it is not necessary to spend time with thiskind of setting, so it is extremely easy to formulate a method, andmanageability when executing the method can be made extremely good.

[Modified Example]

Another example embodiment of the present invention created mainly bychanging the example embodiment described above will now be illustrated.

When estimating the thermal displacement according to the first exampleembodiment, the detected temperatures of the temperature sensors may beestimated temperatures expressed by [Expression 7] below. Here, O_(i, t)is the estimated temperature of the estimated element i, O_(i, t-1) isthe estimated temperature of the estimated element i at the time of thelast calculation (and is stored in appropriate storing means), T_(i, t)is the detected temperature of the estimated element i, b is the timeinterval of the calculations, and β_(i) is the constant at the time ofdisplacement of the estimated element i. Also, β_(i) is linked to themachine information, and is automatically selected as a parameter basedon the machine information. Using the estimated temperatures in this waymakes it possible to make a highly accurate correction based on thethermal displacement.

$\begin{matrix}{O_{i,t} = {O_{i,{t - 1}} + {\left( {T_{i,t} - O_{i,{t - 1}}} \right) \cdot \left( \frac{b}{b - \beta_{i}} \right)}}} & \left\lbrack {{Expression}\mspace{14mu} 7} \right\rbrack\end{matrix}$

The machine information may be stored in the correction amountestimating device or the temperature measuring device, or a combinationof these, instead of being stored in the NC device or the displacementtype calculating device, and may be information indicative of acombination of estimated elements instead of being specifications setdistinguishing information. At least two of the correction amountestimating device (the displacement type calculating device), thetemperature measuring device, and the NC device may be combined andintegrated together. The various database data formats and contents maybe in various modes, such as one in which temperature sensor numbers arearranged by machine information in the temperature sensor selectiondatabase of the second example embodiment. The temperature sensorselection according to the second example embodiment may also be appliedin the first example embodiment, and the parameter selection accordingto the first example embodiment may also be executed in the secondexample embodiment. The thermal displacement correcting apparatusaccording to the present invention may also be applied to a machine toolother than a portal machining center.

What is claimed is:
 1. A thermal displacement correcting apparatus for amachine tool comprising: a correction amount estimating portion thatcalculates a thermal displacement correction amount of the machine toolbased on a combination of a plurality of estimated elements, wherein thecorrection amount estimating portion stores collections of parametersfor an estimated thermal displacement calculation as parameter groups,the collections of parameters including a parameter group having atleast one parameter as one of the estimated elements different from theestimated elements of at least another parameter group which does notinclude the at least one parameter, reads machine information todetermine a presence or an absence of the at least one parameter basedon the machine information, when the at least one parameter is present,selects the parameter group for the estimated thermal displacementcalculation including the at least one parameter as one of the estimatedelements, and when the at least one parameter is absent, selects the atleast another parameter group for the estimated thermal displacementcalculation which does not include the at least one parameter, obtainsmeasurements from sensors for parameters in the selected parametergroup, calculates an estimated thermal displacement of each estimatedelement according to the selected parameter group, calculates thethermal displacement correction amount of the machine tool by combiningthe estimated thermal displacements of each estimated element in theselected parameter group, and the thermal displacement correctingapparatus outputs the calculated thermal displacement correction amountto an NC device, and the NC device uses the calculated thermaldisplacement correction amount to correct a movement of a shaft of themachine tool to account for the thermal displacement, thereby increasingan accuracy of a machining of a surface of a workpiece.
 2. A method forcalculating a thermal displacement correction amount of a machine toolbased on a combination of a plurality of estimated elements, the methodcomprising: storing collections of parameters for an estimated thermaldisplacement calculation as parameter groups, the collections ofparameters including a parameter group having at least one parameter asone of the estimated elements different from the estimated elements ofat least another parameter group which does not include the at least oneparameter, reading machine information to determine a presence or anabsence of the at least one parameter based on the machine information,when the at least one parameter is present, selecting the parametergroup for the estimated thermal displacement calculation including theat least one parameter as one of the estimated elements, and when the atleast one parameter is absent, selecting the at least another parametergroup for the estimated thermal displacement calculation which does notinclude the at least one parameter, using sensors to measure parametersfor the selected parameter group, calculating an estimated thermaldisplacement of each estimated element according to the selectedparameter group, calculating the thermal displacement correction amountof the machine tool by combining the estimated thermal displacements ofeach estimated element in the selected parameter group, and outputtingthe calculated thermal displacement correction amount to an NC device,the NC device using the calculated thermal displacement correctionamount to correct a movement of a shaft of the machine tool to accountfor the thermal displacement, thereby increasing an accuracy of amachining of a surface of a workpiece.